In order to support higher data rates and improve spectrum efficiency, new wireless technologies have been developed. For example, the third generation partnership project (3GPP) long term evolution (LTE) system has been introduced into 3GPP Release 8 (R8).
The LTE downlink (DL) transmission scheme is based on orthogonal frequency division multiple access (OFDMA), and the LTE uplink (UL) transmission scheme is based on single-carrier (SC) discrete Fourier transform (DFT)-spread OFDMA (DFT-S-OFDMA) or equivalently, single carrier frequency division multiple access (SC-FDMA). The use of single-carrier transmission in the UL is motivated by the lower peak-to-average power ratio (PAPR) or cubic metric (CM) compared to multi-carrier transmission such as OFDM.
LTE-Advanced (LTE-A) is designed to further improve achievable throughput and coverage of LTE-based radio access systems, and to meet the IMT-Advanced requirements of 1 Gbps and 500 Mbps in the DL and UL directions, respectively. One major feature of LTE-A is bandwidth extension, or component carrier aggregation, and support of flexible bandwidth arrangement. Bandwidth extension allows DL and UL transmission bandwidths to exceed 20 MHz, (e.g., 100 MHz). It also allows for more flexible usage of the available paired spectrum. In LTE-A, operations in contiguous bandwidth aggregation or non-contiguous bandwidth aggregation are possible. Component carrier aggregation may be either symmetric or asymmetric.
One design criteria for LTE-A is to maintain the backward compatibility with LTE. In the LTE system DL direction, wireless transmit/receive units (WTRUs) receive data on the physical DL shared channel (PDSCH). The transmission of the PDSCH is scheduled by the eNodeB using a DL scheduling assignment, which is carried on a physical downlink control channel (PDCCH). As part of the DL scheduling assignment, the WTRU receives control information for the modulation and coding scheme (MCS), DL resources allocation, etc. The WTRU decodes its allocated PDSCH resources on the allocated DL resources.
In the LTE system UL direction, L1/2 control signaling, (such as hybrid automatic repeat request (HARQ) positive acknowledgement/negative acknowledgement (ACK/NACK), channel quality indication (CQI), precoding matrix indication (PMI), rank indication (RI), etc.), needs to be transmitted to support the DL transmissions, UL transmissions, scheduling, multiple-input multiple-output (MIMO), etc. If the WTRU has not been assigned a UL resource for UL data transmission, (e.g., PUSCH), then the L1/2 UL control information is transmitted on a PUCCH. The PUCCH resources are located at the edges of the total available cell bandwidth (BW). FIG. 1 shows transmission of UL control information, (i.e., HARQ ACK/NACK), in response to the reception of PDSCH in the DL in an LTE single carrier system.
The following combinations of UL control information for HARQ ACK/NACK on PUCCH for frequency division duplex (FDD) for single component carrier are supported in LTE: HARQ-ACK using PUCCH format 1a or 1b, HARQ-ACK and scheduling request (SR) using PUCCH format 1a or 1b, and CQI and HARQ-ACK using PUCCH format 2a or 2b for normal cyclic prefix and PUCCH format 2 for extended cyclic prefix.
In an LTE-A system, due to component carrier aggregation, a WTRU may receive multiple codewords via multiple DL component carriers and therefore it may be required to feed back multiple PUCCHs for HARQ ACK/NACKs in response to the reception of multiple PDSCHs in the multiple DL component carriers. However, transmitting multiple PUCCHs simultaneously may increase a CM or PAPR. This is an issue particularly in the power limited cases, such as for low power class WTRUs or when WTRUs are at cell edge. This also causes a coverage problem due to the transmit power backoff of the power amplifier at the WTRU.